The automobile industry has forever strived to design vehicles with improved traction, handling and cornering capabilities. It is clear that four-wheel drive offers improved vehicle handling on rough surfaces and under poor traction conditions. Now four-wheel steering which has been recently introduced on the automobile market is touted as a significant advance in cornering capabilities. Perhaps the most significant progress has been achieved in the design of tires which are capable of maintaining a substantial tractive force under sharp cornering slip angle conditions and high speed. Today's most automobile tires can retain an available tractive force of up to 300 Kg during cornering maneuvers at slip angles of 5 to 10 degrees and under cornering forces in excess of 200 Kg. One may say that this available tractive force is greatly under-utilized particularly on the rear wheels of a conventional front-steered road vehicle
Besides the conventional differential which shifts the torque applied to a driving pair of wheels from the inner wheel to the outer wheel, the only torque controlling mechanism currently in use are limited to the anti-brake locking systems and wheel spin control apparatus. An example of the former is disclosed in U.S. Pat. No. 4,718,736 Fennel et al., and the latter is typified by the disclosure of U.S. Pat. No. 4,762,196 Harada et al. However, those two mechanisms are not directly intended to assist the vehicle in cornering or any other attempt to steer the vehicle. While these advance systems monitor the steering wheel angle, speed and lateral or longitudinal accelerations, it is only for the purpose of modifying the threshold above which the system becomes effective. In fact, these mechanisms are specifically designed to avoid any change of direction of the vehicle that might result from excessive braking or wheel spinning actions.